Method for the direct conversion of methane to aromatic hydrocarbons



Nov. 12, 1968 R. A. SANCHEZ 3,410,922

. METHOD FOR THE DIRECT CONVERSION OF METHANE TO AROMATIC HYDROCARBONS 2 Sheets-Sheet 1 Filed Nov. 14, 1966 INVENTOR.

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METHOD FOR THE DIRECT CONVERSION OF METHANE T0 AROMATIC HYDROCARBONS Filed NOV. 14, 1966 2 Sheets-Sheet 2 z Mam/7H4; 4w:

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7m: (Haves) 645E001 MMZS MIL? CA? V mvwroa 2054-274 54NCHZ Jrraeuezs United States Patent 3,410,922 METHOD FOR THE DIRECT CONVERSION OF METHANE T0 AROMATIC HYDROCARBONS Robert A. Sanchez, Del Mar, Calif., assignor to The Salk Institute for Biological Studies, San Diego, Calif a corporation of California Filed Nov. 14, 1966, Ser. No. 594,184 27 Claims. (Cl. 260-673) ABSTRACT OF THE DISCLOSURE A process for the direct production of an aromatic hydrocarbon and, particularly naphthalene, from methane comprising the steps of l) cooling the walls of a reaction chamber to a temperature substantially below the melting point of the aromatic hydrocarbon; (2) introducing methane into the reaction chamber; and (3) heating the methane in said reaction chamber to a temperature between about 800 C. and about 2000 C. such that the heating of the methane does not appreciably heat the cooled walk of the reaction chamber to thereby condense out the aromatic hydrocarbon on the walls of the reaction chamber. Preferably, the heating step is carried out by passing a current through a filament positioned a spaced distance from the walls of the reaction chamber.

This invention relates generally to the production of aromatic organic compounds from methane and, more specifically, to the direct production of naphthalene from methane.

Heretofore, naphthalene has been produced both synthetically, e.g., in the cracking of petroleum, and from natural sources, e.g., from coal tar. However, production of naphthalene by synthetic means has proved to be uneconomical because of the low yield (about 1%) of naphthalene from low molecular weight aliphatic compounds. Thus, naphthalene is produced, at present, almost entirely from natural sources such as coal tar. Because of the need for synthetic processes in national emergencies, for example, during wartime, and because of the present relatively high cost of synthetically produced naphthalene, it would be highly advantageous to have a synthetic process for the production of naphthalene from methane, especially if such process was relatively simple and economical. It would also be of advantage if such a process could, with slight modification, be employed to produce other aromatic compounds such as benzene.

In view of the foregoing limitations in the prior art, it is a major object of this invention to provide a simplified and inexpensive process for the direct, eflicient and highyield conversion of methane to selected aromatic compounds such as naphthalene or benzene.

It is a further object of this invention to provide a process for synthetically producing naphthalene from methane which is capable of producing a substantially higher yield of naphthalene than can be produced from presently known synthetic methods' It is a still further object of this invention to provide a process for directly producing one of naphthalene, benzene, or another aromatic compound from methane in a form which is relatively free from other organic conversion products of methane.

It is an even further object of this invention to provide a process for the direct conversion of methane to naphthalene by either batch or continuous operations.

It is yet another object of this invention to provide a process for the direct conversion of methane to other aromatic compounds e.g., benzene by simple modifications of the process of this invention.

Other objects and advantages of the process of this invention will become apparent from following description and from the drawings in which:

FIGURE 1 is a graphical representation of the yield of naphthalene as a function of the reaction chamber wall temperature at a constant methane heating temperature;

FIGURE 2 is a graphical representation of the change in total vapor pressure in the reaction chamber as a function of time;

FIGURE 3 is a graphical representation of the increase in yield of naphthalene as a function of time; and

FIGURE 4 is a sectional view of an apparatus for practicing the method of this invention as a continuous process.

It has now been found that the direct conversion of methane to aromatic compounds in economically feasible quantities can be obtained by heating methane above about 800 C. in a reaction chamber when the walls of the reaction chamber are simultaneously cooled to substantially below the melting point of the aromatic compound being produced. By selecting various wall temperatures, a number of aromatic compounds can be produced as a product which is relatively free from contamination by other reaction products as compared with prior art synthetic processes. Additionally, where naphthalene is being produced, the yield of naphthalene is substantially higher than that obtained by prior art synthetic processes of which we are aware.

The reasons for the relatively high conversion of methane to aromatic compounds, and especially naphthalene, is not completely understood. However, it is believed that the use of a heated reaction zone in close proximity to a cooled or condensation zone enables the aromatic compound to be drawn off from the reaction mixture shortly after being produced, thereby substantially eliminating yield-reducing reactions involving the aromatic product. Furthermore, because of the control exercisable over the wall temperature, substantially only the desired product is condensed out onto the walls, thereby causing other products to continue reacting and producing more of the desired aromatic product. Thus, significant yields of various aromatic products can be obtained merely by changing the wall temperature while maintaining a substantially constant reaction temperature.

The direct conversion of methane to naphthalene will first be described. Thereafter, modifications in the meth ane to naphthalene process which permit production of other aromatic compounds will be described. The process as described by the following steps (1), (2) and (3) will hereafter be described as the naphthalene process or naphthalene process of this invention.

In general, the naphthalene process comprises the steps of: (1) cooling the walls of a reaction chamber substantially below the melting point of naphthalene; (2) introducing a volume of methane into the reaction chamber; (3) while maintaining the chamber wall temperature substantially below the naphthalene melting point, heating the methane, within a localized heating zone, to a temperature between about 800 C. and about 2000" C. for a predetermined time sufficient to produce a substantial yield of naphthalene; and (4) removing the reaction product condensing out on the cooled chamber walls and recovering, by known methods, the naphthalene from the product. Hereafter, the reaction product formed on the reaction chamber walls will be designated as condensate or condensate product whether such product is liquid or solid.

In the cooling step (1), the reaction chamber is immersed in a bath which can be held substantially below the melting point of naphthalene (melting point of naphthalene is about C.) throughout the reaction. An ice and water bath provides the required temperature control and reaction chamber wall temperature in the production of naphthalene, the temperature thus produced at the chamber wall being about C. When other aromatic compounds are being produced, other low-temperature producing bath components may be employed. For example, to lower the reaction chamber wall temperature substantially below the melting point of benzene, a bath consisting of Dry Ice and acetone may be employed.

Satisfactory yields of naphthalene can be obtained within a range of wall temperatures, the upper limit of which temperature range lies substantially below the melting point of naphthalene. It has been found that below and above this temperature range, the yield of naphthalene decreases significantly. Thus, it is preferable to maintain the reaction chamber wall temperature between about l0 C. and about 30 C. for optimum yields of naphthalene. Above the upper temperature limit, the yield of naphthalene decreases because less product is trapped on the walls due to the higher naphthalene vapor pressures. Below the lower temperature limit, the naphthalene yield decreases because certain intermediate products which react to form naphthalene in the heated zone of the reaction chamber, condense out on the chamber walls at these lower temperatures.

The foregoing temperature limits are graphically illustrated in FIGURE 1 with respect to naphthalene production. The data of FIGURE 1 were produced as described in Examples 1, 2, 3 and 4. Briefly, the test to determine each point comprised: substantially evacuating a flask, introducing methane into the evacuated flask, cooling the walls of the flask to the desired temperature and, locally heating the methane by passing a current through a tungsten filament inserted in the flask. Gas chromatographic analysis was used to determine yield of naphthalene as a percent of the theoretical yield.

From FIGURE 1, it can be seen that the yield of naphthalene decreases somewhat as the temperature increases above about 0 C. or decreases below about 0 C. It can further be seen that below about C. and above about 30 C., the yield of naphthalene is significantly lower than when the wall temperature is between about l0 C. and about 30 C. That is, small wall temperature changes between about -10 C. and about 30 C. produce substantial changes in the yield of naphthalene whereas the same wall temperature changes above and below this range produce relatively small changes in the yield of naphthalene.

After the reaction chamber wall temperature has been reduced or While the wall temperature is being reduced to the desired temperature, methane is introduced into the reaction chamber (step 2). If the naphthalene process is continuous, it i preferable to purge the air from the reaction chamber by passing methane through the system. Where the naphthalene process is a batch process, it is preferable to evacuate the air and/or other contamination by drawing a vacuum on the chamber before introducing methane.

If the reaction chamber is not completely purged of the air and other contaminants, the yield of naphthalene may be reduced. For example, oxygen can react with the methane to produce some carbon dioxide, carbon monoxide and water thereby decreasing the amount of methane available for the production of naphthalene. Therefore, it is preferable to substantially completely evacuate contaminants from the reaction chamber prior to initiating the methane-naphthalene reaction. However, it has been found that the effect of contaminants, such as oxygen, is relatively small. Therefore, great care need not be taken to remove these contaminants from the reaction chamber in so far as the production of naphthalene is concerned, although contaminants such as oxygen should be removed where filament metals which readily combine with oxygen are being used to thereby extend the lives of such filaments.

For the reasons described above with respect to contaminants, the methane may be ultra-pure methane or it may be standard line gas. If the line gas contains hydrogen,

the conversion of methane to naphthalene, as described by will be somewhat reduced due to the reversible nature of the reaction.

It will be understood that steps (1) and (2) may be reversed, that is, the methane may be introduced into the reaction chamber prior to cooling the chamber walls.

After the reaction chamber has been charged with methane and after the walls of the reaction chamber have been cooled to the desired temperature, the heating step (3) can be initiated. Heating of the methane may be accomplished by any convenient means. However, the heating means chosen must not appreciably interfere with the cooling of the chamber walls. That is, the methane must be heated so that negligible amounts of heat are absorbed by the reaction chamber walls. If the wall temperatures cannot be controlled within the desired temperature range, the yield of naphthalene will be decreased for the reasons stated heretofore in connection with the wall temperature limits. Therefore, to avoid heating the chamber walls, heating of the methane gas must be localized, that is, substantially confined to a limited zone within the total methane volume.

To provide localized heating, it is preferable to employ a filament consisting of a thin piece of metal capable of withstanding temperatures up to about 2000 C. for a sufficiently long time to enable the reaction to be completed, that is, until substantially no more naphthalene is produced. Tungsten and a ferrous-aluminum alloy (containing 22% Cr, 4.5% A1, 0.5% Co, 73% Fe) designated Kanthal D (manufactured by Kanthal Corp., Conn.) have been successfully used as the filament metal.

The temperature to which the methane is heated may vary from about 800 C. to about 2000 C. Below about 800 C., naphthalene will not form from methane as described by Equation 1. Above about 2000 C., substantial amounts of hydrogen are boiled off the organic compounds thereby leaving a residue of carbon. Preferably, the heating step (3) is carried out in a temperature range of about 1000 C. to about 2000 C. and, more preferably, at a temperature of about 1500 C. The rate of conversion of methane to naphthalene in the 1000 C.- 2000 C. range is higher than in the 800 C.l000 C. range. At a temperature of about 1500 C., there is an optimum balance between rate of reaction and loss of material through carbonization.

It has been found that the yield of napthalene can be increased by cycling the temperature of the gases, that is, by alternately increasing and decreasing the heating temperature. It is not presently known why cycling the heating temperature produces a higher yield of naphthalene as compared to the constant heating temperature method, A possible reason is that during the gas cooling periods, the gas molecules collect on the heating element such that when the heating temperature is increased these molecules interact more efficiently than when dispersed throughout the reaction chamber. However, regardless of the theoretical reason, heating temperature cycling does substantially improve the yield of naphthalene.

When employing a filament as the heating element, temperature cycling is accomplished by periodically cutting off the current through the filament. The ratio of the time that the current passes through the filament in each cycle to the total cycle time, expressed as a percent, is designated as the percent duty. Thus, if the filament is heated for one-tenth of the total cycle time, a 10% duty cycle is being used.

As more fully described in Example 6, a test made using a 10% duty cycle (wall temperature=2.5 C.; heated filament temperature :1500 C.) produced a naphthalene yield of 19.2% and, as more fully described in Example 5, a test using a 25% duty cycle (wall temperature :0 C.; heated filament temperature zl500 C.) produced a yield of about 16%. These yields are to be compared with yields of about using a 100% duty cycle (continuous heating) with similar heating and wall temperatures. Thus it can be seen that increases in the yield of naphthalene of from about 50% to about 100% can be obtained by cycling the heating temperature.

However, it will be understood that as the heating portion of the cycle is decreased to very small fractions of the total cycle time (on the order of about 3 5% the benefit to be derived from cycling will materially decrease. Additionally, as the cycle approaches a 100% duty cycle, the benefits from cycling will decrease, The advantages of cycling can be obtained for cycles between about a 5% duty cycle and about a 20% duty cycle.

Heating is continued for a time sufficient to complete the conversion of methane to naphthalene. The reaction is complete when, by empirical determination, no further changes in certain reaction parameters occur. To determine when the reaction is complete, various methods may be used. For example, the total vapor pressure of the reactants and products may be monitored as the reaction progresses. As shown by Equation 1, the volume of product gases exceeds the volume of reactant gases. Thus as the reaction progresses, the total pressure in the reaction chamber will increase. Completion of the conversion of the conversion of methane to naphthalene is evidenced by a substantially constant reaction chamber vapor pressure.

This aforedescribed increase in vapor pressure is graphically illustrated by FIGURE 2, which is a typical vapor pressure curve for the herein-described process of converting methane to naphthalene. At time=0, the vapor pres sure of methane and some of the unexpelled air in the reaction chamber was 500 mm. Hg. The chamber was then cooled in an ice bath to 10 C. and the vapor pressure dropped to 450 mm. Hg.

Heating was then commenced and this was immediately followed by a rapid increase in vapor pressure as naphthalene and hydrogen were evolved. As the reaction approached completion the vapor pressure slowly leveled off at an approximately constant value.

In general, the conversion of methane to naphthalene is completed in from 2 to 3 hours in a batch process. The increase of naphthalene with time approximately defines a parabolic relation, with an initially rapid increase in naphthalene yield followed by a gradual decrease in naphthalene production rate. Thus a naphthalene yield vs. time curve approximates in shape the aforedescribed vapor pressure vs. time curve (FIGURE 2). A representative plot of naphthalene yield vs. time is graphically illustrated by FIGURE 3. The data of FIGURE 3 were produced from runs conducted at a wall temperature of about 0 C. and a filament temperature of about 1500 C. (40 v., GB. 110 v./ 150 w. extended service bulb).

After the reaction has been completed, the product condensing out on the reaction chamber walls is collected by, for example, solvent extraction. The dissolved product is then separated into its component constituents by any convenient method to produce pure naphthalene.

The aforedescribed steps (1), (2), (3) and (4) may be performed as a continuous or a batch process. If the process is a batch process, the operating conditions are substantially as described. However, if it is desired to operate a continuous process, the yield of naphthalene will be substantially reduced if provision is not made to increase the dwell time, that is, the time during which the methane is being heated. For example, it has been found, experimentally when employing the same test conditions except for methane flow rate that when the methane flow rate was increased threefold, the yield of naphthalene decreased to one-third'of the naphthalene yield at the lower flow rate. Thus, from the foregoing example, it will be seen that provision must be made in a continuous process for retaining the reactants in the heated zone of the reaction for a time suflicient to provide naphthalene yields equivalent to batch process yields.

A continuous process apparatus for providing suflicient reactant dwell time is shown in FIGURE 4 wherein the numeral 10 designates such an apparatus. The apparatus 10 comprises a reaction chamber 11 and a housing 12 ex tending therefrom. The bottom of the housing forms a liquid product collecting chamber 13 from which there extends a liquid exit line 14. The reaction chamber 11 has reactant inlet line 15 and gaseous product exit line 16 attached thereto. A heating element 17 is located within the reaction chamber 11 and is suitably connected to a power source (not shown). Rotatably mounted on a shaft 18 is drum 19 which is adapted to be cooled to the desired temperature. Flexible brushes 20 are mounted on a perforated plate 21 located within the liquid collection chamber 13 so that products condensing on the cooled drum 19 can be removed therefrom by contact with the brushes 20.

In operation, methane is fed into the reaction chamber and reacts to produce naphthalene, hydrogen and various intermediate products. The naphthalene condenses out of the reaction gases onto the cooled drum 19 and is carried around to the brushes 20 where it is: deposited into the liquid collection chamber 13 and exists through the line 14. The gaseous products are removed through the gas line 16.

Thus far, the process of this invention has been described for the direct production of naphthalene from methane. However, with certain modifications, which are described hereafter, the aforedescribed process can be used to produce aromatic compounds other than naphthalene.

The first modification concerns the cooling of the reaction chamber walls. As With naphthalene, the chamber walls must be cooled substantially below the melting point of the desired aromatic product. However, the temperature range to which the chamber walls are to be cooled and the temperature distance of that range below the melting point of the desired aromatic will vary from those temperature figures given for the naphthalene process. As the wall temperature is reduced, greater amounts of undesired product will con-dense out with the desired product. Thus, it will be necessary, in each case, to balance the use of higher wall temperatures to reduce the amount of undesired product condensing out and the use of lower wall temperatures to increase the amount of desired product condensing out. For example, it has been found that benzene yields of 1l%12% can be produced at wall temperatures between about -70 C. and about C.

The heating range to produce aromatics other than naphthalene is also between about 800 C. and about 2000 C. However, it has been found that greater fluctua tions in the yield of the non-naphthalene aromatics, as compared with naphthalene, are produced by changes in the heating temperature.

Collection of the non-naphthalenic aromatic product may also be accomplished by solvent extraction. However, the separation step will be somewhat more complex than for naphthalene because of the greater number of constituents in the product when low chamber wall temperatures are used.

As will be apparent from the foregoing description, both the desired aromatic hydrocarbon product and hydrogen are formed from the pyrolysis of methane. Therefore, these products may be used as intermediates in the formation of hydrogenated aromatic compounds by reacting these products in the presence of a catalyst. For example, naphthalene and hydrogen, produced as described, may be reacted at elevated temperatures in the presence of a suitable catalyst to produce tetrahydronaphthalene.

The method of this invention will be further described by the following examples.

7 EXAMPLE 1 This example illustrates the formation of naphthalene from methane when the reaction chamber wall temperature is cooled to about 10 C.

A standard 500 ml. boiling flask, having a tungsten filament inserted therein, Was substantially evacuated and methane was introduced to a pressure of 499 mm. Hg at room temperature. The filament was a 300 watt extended service filament. The flask was cooled to about 10 C. in an ice-alcohol bath. Fifty volts were applied to the filament to produce a heating temperature of about 1500 C. Heating was continued for 2 hrs. 40 min.

Throughout the run, the total vapor pressure in the flask is monitored. The resulting vapor pressure-time curve is graphically illustrated in FIGURE 2.

At the end of the run, the product which had condensed out on the flask walls was dissolved in ether. Using a gas chromatograph to analyze the product it was determined that the naphthalene yield was about 4.2%. The yield was slightly lower than expected from the vapor pressure-time curve because the test concluded prematurely due to a broken hose which admitted air to the flask.

EXAMPLE 2 This example illustrates the production of naphthalene at the same reaction temperature as used in Example 1 but at a higher wall temperature C.).

A 250 ml. flask, containing a GE. 110 v./150 Watt extended service filament, was substantially evacuated. Methane was then introduced to a pressure of 750 mm. at room temperature and heating was commenced by placing 40 volts across the filament. Heating continued for about 2.0 hours.

Analysis of the product disclosed a napthalene yield of 10.3%.

EXAMPLE 3 This example illustrates the conversion of methane to naphthalene at about the same reaction temperatures as in Examples 1 and 2, but at a wall temperature of about 23 C.

The apparatus employed was the same as described in Example 1. The procedure was also the same as described in Example 1 except that methane was introduced to a pressure of 500 mm. Hg at 23 C. A plot of vapor pressure vs. time indicated that the conversion of methane to naphthalene was complete after about 2.5 hours.

Analysis disclosed a naphthalene yield of 8.64%.

EXAMPLE 4 This example illustrates the effect of decreasing the reaction wall temperature to about 78 C.

The apparatus used was the same 'as described in Example 1. The procedure was also the same as described in Example 1 except that the flask was cooled in an acetone-Dry Ice bath at about -78 C. and heating Was continued for 4.5 hours.

A vapor pressure vs. time plot indicated that the conversion of methane to benzene was substantially complete after about 2.0 hr. Analysis of the product disclosed a yield of benzene of 11.4% of theoretical and a yield of naphthalene of 1.0%.

EXAMPLE 5 This example illustrates the increased yield obtainable by cycling the heating temperature.

The apparatus was the same as described in Example 1 with the addition of a timer to alternately start and stop the flow of current through the filament. After the flask was evacuated and filled with a known amount of methane, it was cooled in a 0 C. ice bath. The filament was connected to a fifty volt source, and the timer was set for a 25% duty cycle and heating was commenced. The duration of the heating could not be determined because the filament burned out during the night.

Analysis of the product disclosed a yield of naphthalene of about 15.7%.

EXAMPLE 6 This example further illustrates the increased yield of naphthalene derived from cycling the heating temperature.

The apparatus was the same as in Example 2 except that a timer was connected to the filament. Additionally, the procedure was the same as in Example 5 except that the timer was set for a duty cycle and the flask was cooled to about 2.5 C. The run lasted for a total of 43 hours (4.3 hours heating time).

The yield of naphthalene was 19.2%.

EXAMPLE 7 This example illustrates the effect of cycling the heating temperature but at a very low duty rating (3.6%).

The apparatus and procedure were as described in Example 5, except that a 3.6% duty cycle was used. The test ran for a time which produced a total heating time of 1 hr. 28 min. Crystals did not form on the wall until about 5 hours had elapsed as compared with the appearance of crystals in Example 5 after only a few minutes.

The yield of naphthalene was about 6.8%.

EXAMPLE 8 This example illustrates the effect of using a ferrousaluminum alloy metal (Kanthal D) as the filament metal.

The apparatus was the same as described in Example 1 except that the filament was made from 30 gauge (0.010 in.) Kanthal D wire having a resistance of 8.1 ohms/foot. The flask was substantially completely evacuated, filled with a measured amount of methane and heating was commenced at a temperature slightly higher than that used in Example 1. Heating continued for minutes at which time the filament burned out.

The yield of naphthalene was 4.3

From the foregoing description and examples it will be apparent that a unique method for directly producing aromatic hydrocarbons, such as benzene and naphthalene from methane has been described. For example, hereindescribed naphthalene process is capable of producing yields of naphthalene of up to about a substantial increase over the prior art methods. The high yields of naphthalene are apparently produced by the physicallyclose combination of a heating zone (800 C.2000 C.) and a cooling or condensing zone maintained at a temperature (-10 C. C.) substantially below the melting point of naphthalene such that naphthalene is selectively condensed out at the cooling zone shortly after it is formed but such that the undesired products are returned to the heating zone.

As described, various high temperature metals are utilized for the filament wire which is used to supply heat in the heating zone. Additionally, the apparatus may be modified to provide either a batch or a continuous process.

While certain embodiments are disclosed herein, modifications which lie within the scope of this invention will occur to those skilled in the art. Therefore, I intend to be bound only by the scope of the claims which follow.

I claim:

1. A process for the direct production of an aromatic hydrocarbon from methane comprising the steps of:

cooling the walls of a reaction chamber to a temperature substantially below the melting point of said aromatic hydrocarbon;

introducing methane into said reaction chamber; and

heating said methane in said reaction chamber to a temperature between about 800 C. and about 2000 C. and about 2000 C. such that said heating of said methane does not appreciably heat said cooled walls of said reaction chamber, whereby said aromatic hydrocarbon is produced and condenses out on said walls of said reaction chamber.

2. The process of claim 1 wherein said aromatic hydrocarbon is benzene.

3. The process of claim 2 wherein said temperature of said walls of said reaction chamber is between about 70 C. and about 80 C.

4. The process of claim 1 wherein said aromatic hydrocarbon is removed from said walls of said reaction chamber by solvent extraction.

5. The process of claim 1 wherein the air in said reaction chamber is substantially evacuated before said introduction of said methane.

6. The process of claim 1 wherein said heating is continued until substantially no further change in the total vapor pressure in said reaction chamber occurs.

7. The process of claim 1 wherein said methane is continuously introduced into said reaction chamber and wherein said methane remains in said reaction chamber for a time suflicient to complete the conversion of said methane to said aromatic hydrocarbon.

8. The process of claim 1 wherein said heating is accomplished by passing a current through a filament which is located a spaced distance from the walls of said reaction chamber.

9. A process for the direct production of naphthalene from methane comprising the steps of:

cooling the walls of a reaction chamber to a temperature substantially below the melting point of naphthalene;

introducing methane into said reaction chamber; and

heating said methane in said reaction chamber to a temperature between about 800 C. and about 2000 C. such that said heating of said methane does not appreciably heat said cooled walls of said reaction chamber, whereby naphthalene is produced and condenses out on said walls of said reaction chamber.

10. The process of claim 9 wherein said condensed naphthalene is removed from said reaction chamber by solvent extraction.

11. The process of claim 9 wherein said reaction chamber is cooled to a temperature between about -l C. and about 30 C.

12. The process of claim 9 wherein substantially all of the air within said reaction chamber is removed prior to said introduction of said methane into said reaction chamber.

13. The process of claim 9 wherein said methane is heated to a temperature between about 1000" C. and

about 2000 C.

14. The process of claim 9 wherein said methane is heated by cycling the heating temperature by alternately heating and not heating said methane.

15. The process of claim 9 wherein said heating is continued until the conversion of said methane to said naphthalene at said heating and said cooling temperatures is substantially complete.

16. The process of claim 9 wherein said heating is continued until substantially no further change in total vapor pressure in said reaction chamber occurs.

17. The process of claim 9 wherein said methane is continuously introduced into said reaction chamber and wherein said methane remains in said reaction chamber for a time sutficient to complete the conversion of said methane to said naphthalene.

18. The process of claim 13 wherein said methane is heated to a temperature of about 15 00 C.

19. The process of claim 14 wherein said heating cycle varies from about a 5% duty cycle to about a 20% duty cycle.

20. A process for the direct production of naphthalene from methane comprising the steps of cooling the walls of a reaction chamber to a temperature lying between about 10 C. and about 30 C.;

introducing methane into said reaction chamber, said reaction chamber being substantially free of oxygen; and heating said methane in said reaction chamber at a. temperature between about 1000 C. and about 2000 C. such that said heating does not appreciably heat said cooled walls of said reaction chamber, whereby said naphthalene is produced and condenses out on said walls of said reaction chamber. 21. The process of claim 20 wherein said methane is heated by cycling the heating temperature by alternately heating and not heating said methane.

22. The process of claim 20 wherein said heating of said methane is continued until substantially no further change in the total vapor pressure within said reaction chamber occurs.

23. The process of claim 20 wherein said methane is continuously introduced into said reaction chamber and wherein said methane remains in said reaction chamber for a time sufficient to complete the conversion of said methane to said naphthalene.

24. A process for producing naphthalene directly from methane comprising the steps of cooling the walls of said reaction chamber to a temperature between about -10 C. and about 30 C.;

introducing methane into said reaction chamber, said reaction chamber being essentially free of oxygen; and

heating said methane in said reaction chamber by passing a current through a filament sufiicient to heat said methane to a temperature between about 800 C. and about 2000 C., said filament being located a spaced distance from the walls of said reaction chamber and being capable of withstanding temperatures of between about 800 C. and 2000 C., whereby naphthalene is produced and condenses out on said walls of said reaction chamber.

25. The process of claim 24 wherein said filament is tungsten.

26. The process of claim 24 wherein said filament is a substantially ferrous-aluminum alloy.

27. The process of claim 24 wherein said heating temperature is cycled by alternately commencing and stop ping the flow of said current through said filament, to thereby increase the yield of said naphthalene.

References Cited UNITED STATES PATENTS 8/1926 Snelling 23209.3 3/1965 Jenny 260-623 

